In wireless communication networks, UEs (User Equipments), communicate data via radio base stations.
When communicating data, DL (Downlink) data is sent from radio base stations to UEs, and UL (Uplink) data is sent from UEs to radio base stations. To enable the radio base stations and the UEs to exchange UL data and DL data between each other, they both comprise transceiver arrangements and antennas.
In this description, the term “User Equipment” will be used to denote any suitable communication terminal adapted to communicate with a radio base station. A UE may be implemented as a mobile phone, a PDA (Personal Digital Assistant), a handheld computer, a laptop computer, etc. A “radio base station” may be implemented as a NodeB, an eNodeB, a repeater, etc.
With reference to FIG. 1, which is a schematic block diagram, a communication scenario will now be described according to the prior art.
In a RAN (Radio Access Network) 100, a UE 102 is present to exchange data with a core network 108 via a radio base station 104, e.g. a NodeB. Transceivers of as well the UE 102 and the radio base station 104 comprise transmitter parts and receiver parts. Some examples of transceiver arrangements will be further disclosed below.
In order to enable transceivers to compensate for irregularities of included components, especially non-linearity of power amplifiers, commonly specific transmitter observation receivers (TORs) have been arranged in the transceivers. These TORs analyses the TXRF (Transmitter Radio Frequency) signal spectrum and provides feedback to the transmitters of the transceiver.
Receivers of transceivers are typically implemented as homodyne receivers or heterodyne transceivers.
In “homodyne” receiver, a received RF signal spectrum is directly frequency converted to zero frequency or near to zero frequency range. By mixing the received RF signal spectrum with a local oscillator output frequency which is identical to, or very close to the carrier frequency of the intended signal spectrum. The frequency converted signal spectrum is then applied to a demodulator which gives baseband signals out, before being A/D (Analogue-to-Digital) converted and fed into the receiver arrangement. By performing only a single frequency conversion, the basic circuit complexity is reduced but other issues arise, for instance, regarding dynamic range, and against blocking performance.
In “heterodyne” receiver structures, an incoming RF-signal is fed into a mixer where it is mixed with a local oscillator (LO) frequency. The mixer output is a down-converted version of the RF-signal of an intermediate frequency, i.e. the RF-signal spectrum is transferred into an IF (Intermediate Frequency) spectrum.
Also RXRF (Receiver Radio Frequency) signal spectrums may be observed and analysed in order to achieve an increased performance of the receiver. However, the major task is to enable the receiver to compensate for noise and interference, which is e.g. introduced by nonlinear circuits, such as amplifiers and mixers which receive the RXRF signal spectrums. Some basic of an ROR (Receiver observation receiver) is that it should be more linear than the receivers themselves.
With reference to FIG. 2, which is a schematic overview, a transceiver according to the prior art will now be described.
The transceiver 200 is a TDD (Time Division Duplex) transceiver and comprises a transmitter 202, a receiver 204, an antenna port 206, and a baseband unit 208. The transmitter 202 is arranged to convert a TX (Transmitter) baseband of the baseband unit 208 into an RXRF signal spectrum. In the transmitter 202, the baseband is subject e.g. to digital-to-analog conversion (DAC), frequency shifting, and amplifying (PA), which result in a RXRF signal spectrum. The antenna port 206 is arranged to transmit the RXRF signal spectrum via an antenna. At the antenna port 206, the RXRF signal spectrum is filtered in a band-pass filter of a filter unit (FU). A TOR (Transmitter Observation Receiver) 210 is further arranged to frequency shifting the RXRF signal spectrum, before analog-to digital converting (ADC) the frequency shifted RXRF signal spectrum and input to the baseband unit 208. The baseband unit 208 will then get feedback regarding the characteristics of the transmitter 202 and its various components. For instance, the baseband unit 208 may be aware of non-linearities of the PA, and may for instance introduce or adjust DPD (Digital Pre-Distortion) of the baseband signal spectrum before being fed to the input of the transmitter 208.
The receiver 204 is arranged to convert an RXRF signal spectrum which is received from the antenna via the antenna port 206 and convert into an RX baseband signal spectrum. The receiver 204 comprises an LNA (Low Noise Amplifier) and an RX block. The power of the RXRF signal spectrum is low and due to large gain of the LNA the amplified RXRF signal spectrum is typically affected substantial amount of noise. A ROR (Receiver Observation Receiver) 212 is further arranged in parallel with an RX block of the receiver 204, to enable the baseband unit 208 to get feedback regarding the characteristics of the components of the receiver 204. For instance, the baseband unit 208 may be aware of various gains of the RF LNA block and the RX block, as well as the current interference situation.
The basic concept of as well the TOR and the ROR is that they comprise local oscillators and A/D-converters arranged to mix the TXRF and RXRF spectrums, respectively. TORs have been traditionally been used, but the need for RORs is quite new. In addition, the requirements of TORs and RORs are quite different. For TORs, the input power, i.e. the power of TXRF is high and the dynamic range is low. For RORs, on the other hand, the power of the RXRF is low and the dynamic range is high. One problem is also that the local oscillators of the TOR and the ROR may disturb each other. Especially, the LO of the ROR is sensitive to disturbances from the LO of the TOR.
As stated, this example relates to a TDD transceiver. However, the situation for an FDD (Frequency Division Duplex) transceiver is similar. One difference is however, that the RXRF signal spectrum and the TXRF signal spectrum have different carrier frequencies. Therefore, the filtering unit (FU) of an FDD transceiver comprises one further band-pass filter, and the LO (Local Oscillator) output frequencies of the TOR 210 and the ROR 212 differ.
In general, components of transmitters and receivers, such as power amplifiers, etc. are expensive to manufacture within reasonable tolerances. Typically, characteristics of power amplifiers are not linear for large gains. In order to compensate for non-linearities and other non-ideal characteristics, transmitters are therefore often provided with so called Transmitter Observation Receivers, which monitors the TXRF (Transmitter Radio Frequency) signal spectrum of the transmitter.
In homodyne transceivers arrangements, also the RXRF (Receiver Radio Frequency) signal spectrum of the receiver are observed, especially for enabling the transceiver to compensate for a large dynamic range of input power.
There is a need to achieve an efficient and flexible solution to control transceivers.